The overall goal is to gain an understanding of the role of the alternative excision repair (AER) pathway in the reversal of DNA damage. A great deal of information was gained during the previous funding period which indicates that the AER pathway in the fission yeast Schizosaccharomyces pombe functions in the repair of a diverse group of DNA lesions ranging from UV bi-pyrimidine photoproducts to base mismatches. An emphasis will be placed on the functions of the AER initiating endonuclease Uve1p in S. pombe. In addition, further refinement of the known Uve1p-related pathways identified in the previous project will be pursued. The scope and focus of the present proposal is expanded considerably from the previous emphasis on UV damage. This is necessary in order to begin to define the multiple potential interrelationships between Uve1p and other DNA repair/processing pathways. Biochemical characterization of the components of the AER pathway and potentially related pathways will continue as well as studies aimed at determining the range of organisms which utilize Uve1p-like proteins for DNA repair.